1. Field of the Invention
The present invention relates to an image processing system having a function of inputting an image by using a line sensor having linearly arranged sensors, and more particularly to an image input apparatus (so-called scanner) for scanning an original color image carried on a paper, a film or the like.
2. Description of the Related Art
A line scanner with a line sensor for scanning an image has been known. For example, Japanese Laid-Open Patent Application Publication No. Hei 5-183674 discloses an image input and output apparatus for storing image data in a memory, and outputting the image data to an external apparatus via a small computer system interface (SCSI) or a general purpose interface bus (GPIB). In this conventional art, the memory serves as a frame memory for storing the data of one image when the image data required by the external apparatus are less than the image data stored in the memory. Further, the memory functions as a buffer memory for storing a part of data of one image when the image data required by the external apparatus are more than the image data stored in the memory. Generally, the larger or the more highly resolved an output image is, the more the data for the output image are. When the output image is highly resolved, all pixels of the input image are stored in the memory. On the other hand, when the outputted image is low resolved, part of the input pixels are extracted and stored in the memory.
FIG. 12 illustrates a conventional method of outputting data to an output apparatus. A memory 201 sequentially stores digital data corresponding to the three primary colors, i.e., red (R), green (G) and blue (B), from the line sensor in the order of R.sub.1, G.sub.1, B.sub.1, R.sub.2, G.sub.2, B.sub.2, R.sub.3, G.sub.3, B.sub.3, . . . . When the digital data are outputted to an output apparatus 202, a set of color data having the same subscript are outputted as the data for one pixel. That is, whenever the color data for one pixel have been outputted from the memory 201, the address pointed by an address pointer is increased by three to output the corresponding data.
In the conventional art described above, when the number of pixels of the external apparatus or the output apparatus (e.g., a display or a printer) is different from that of the image input apparatus, part of the image data are extracted and then stored in a memory in the output apparatus 202 or the like. The extraction is implemented as described below. Suppose .alpha. (a natural number) represents the number of pixels of the output apparatus, and .beta. (a natural number) represents the number of pixels of the input apparatus. The ratio .alpha./.beta. is called the pixel ratio. Suppose N' (a natural number) is the serial number of a pixel to be extracted from the memory. Then N' can be calculated by the equation N'=[N.times.(.beta./.alpha.); N=1, . . . ,.beta.], which is an operation to obtain the largest natural number less than the value calculated by N.times.(.beta./.alpha.). For example, when the pixel ratio is 6/10, the serial numbers of the pixels to be extracted are calculated by putting N=1, . . . , 10, .alpha.=6 and .beta.=10 into the equation [N.times.(.beta./.alpha.)]. Therefore, by the calculation, a series of pixels Nos. 1, 3, 5, 6, 8 and 10 is obtained. However, when such an extraction is implemented, adjacent pixels may be extracted (e.g., 5 and 6 in the above series). That is, there may exist at least one uneven interval in the series except when the pixel ratio is defined by 1/.gamma. (.gamma. is a natural number).
When there is an uneven interval in the series, for example, an inclined line in an image is displayed as a discrete line so that the quality of the image is deteriorated. Therefore, in the conventional art, the pixel ratio can be set only to 1/.gamma. to prevent the deterioration of the image quality. Alternatively, after an image is acquired, the image is corrected by implementing a predetermined interpolating operation between adjacent pixels.
However, when the pixel ratio is limited, the number of the extracted pixels may be too small or too large for the output apparatus. Further, in order to correct the image, an image correction circuit or an image processing software program is required so that the cost of the image processing system will be increased or image processing time will become long.